1. Field of the Invention
The present invention relates to a valve operating system in an internal combustion engine, and more particularly, to a valve operating system in an internal combustion engine, in which the operational characteristic of an engine valve which is an intake valve or an exhaust valve, can be changed in accordance with the operational state of the engine.
2. Description of the Related Art
Such a valve operating system is already known, for example, from Japanese Patent Publication No. 7-107368.
The known valve operating system is constructed so that rocker arms connected to the engine valves, are alternatively switched and driven by a plurality of types of valve operating cams having different cam profiles, wherein the operational characteristic of the engine valves are switched at two or three states in accordance with the operational state of the engine. However, to further enhance the engine performance such as the output torque from the engine, the fuel consumption and the nature of the exhaust gas, it is desirable that the operational characteristic of the engine valves can be finely switched in accordance with the operational state of the engine. In the construction of the known valve operating system, a large number of valve operating cams having the different cam profiles are required, resulting in an increased size of the valve operating system, and hence, it is difficult to realize the valve operating system.